1. Field of the Invention
This invention relates to spiral binder applying machines for calendars, books or the like, and more particularly to the mechanisms for trimming and inwardly bending the ends of the spiral binders.
2. Description of the Prior Art
Biel and Pfaffle U.S. Pat. No. 2,963,049, Pfaffle U.S. Pat. No. 3,826,290 and Pfaffle U.S. application Ser. No. 553,253 filed Feb. 26, 1975, now U.S. Pat. No. 3,924,664, and assigned to the assignee of the present application, show spiral binder applying machines having trimming and bending cutters of this general type. The end trimming and bending operations are accomplished by cutters which descend at opposite ends of the spine and partially envelop and hold turns of the binder so that the cutting blades may accomplish the trimming and bending. Inward bending of the ends is necessary to bridge the gap between the outer and adjacent turns so that, when books are stacked, binders will not snag with each other.
A problem occurs when it is desired to form relatively small diameter coils which have large pitches, that is, greater turn-to-turn spaces. For example, one-quarter inch diameter coil can be made with five turns per inch or four turns per inch, and the latter construction will result in a substantial saving of wire for each binder. However, with less turns per inch (greater pitch), it is necessary to bend a longer end in order to bridge the gap.
The conventional cutting fixtures mentioned above cannot be readily constructed to accomplish this aim, since they cannot be designed to properly envelop and hold the adjacent turns so that the cutting blade may operate.
One solution has been to form one of the two cutter body arms with an inward extension of saw-tooth shape, the cutter having a complementary edge, so that the proper spacing may be achieved. However, this has necessitated manufacturing the cutter body in two pieces which must be later assembled. It also involves providing a relief on one of the body arms for the bend, a construction which is not as desirable as relieving the cutter blade, from the standpoint of design flexibility. This previous construction has been found unsatisfactory from cost and operational standpoints.